Field of the Invention
The present invention pertains to foams and methods for the preparation thereof, and in particular to polyurethane and polyisocyanurate foams and methods for the preparation thereof.
Description of the Related Art
The class of foams known as low density, rigid to semi-rigid polyurethane or polyisocyanurate foams has utility in a wide variety of insulation applications, including roofing systems, building panels, building envelope insulation, spray applied foams, one and two component froth foams, insulation for refrigerators and freezers, and so called integral skin foam for cushioning and safety application such as steering wheels and other automotive or aerospace cabin parts, shoe soles, and amusement park restraints. An important factor in the large-scale commercial success of many rigid to semi-rigid polyurethane foams has been the ability of such foams to provide a good balance of properties. In general, rigid polyurethane and polyisocyanurate foams are known to provide outstanding thermal insulation, excellent fire resistance properties, and superior structural properties at reasonably low densities. Integral skin foams are known to produce a tough durable outer skin and a cellular, cushioning core.
As is known, blowing agents are used to form the cellular structure required for such foams. It has been common to use liquid fluorocarbon blowing agents because of their ease of use and ability to produce foams with superior mechanical and thermal insulation properties. Fluorocarbons not only act as blowing agents by virtue of their volatility, but also are encapsulated or entrained in the closed cell structure of the rigid foam and are generally the major contributor to the low thermal conductivity properties of the rigid urethane foams. The use of fluorocarbon as the preferred commercial expansion or blowing agent in insulating foam applications is based in part on the resulting k-factor associated with the foam produced. The k-factor provides a measure of the ability of the foam to resist the transfer of heat through the foam material. As the k-factor decreases, this is an indication that the material is more resistant to heat transfer and therefore a better foam for insulation purposes. Thus, materials that produce lower k-factor foams are desirable and advantageous.
It is known in the art to produce rigid or semi-rigid polyurethane and polyisocyanurate foams by reacting one or more polyisocyanate(s) with one or more polyol(s) in the presence of one or more blowing agent(s) one or more catalyst(s) and one or more surfactant(s). Water is commonly used as a blowing agent in such systems. Other blowing agents which have been used include hydrocarbons, fluorocarbons, chlorocarbons, chlorofluorocarbons, hydrochlorofluorocarbons, halogenated hydrocarbons, ethers, esters, aldehydes, alcohols, ketones, organic acid or gas, most often CO2, generating materials. Heat is generated when the polyisocyanate reacts with the polyol, and this heat tends to volatilize the blowing agent contained in the liquid mixture, thereby forming bubbles therein as the foaming reaction proceeds. In the case of gas generating materials, gaseous species are generated by thermal decomposition or reaction with one or more of the ingredients used to produce the polyurethane or polyisocyanurate foam. As the polymerization reaction proceeds, the liquid mixture becomes a cellular solid, entrapping the blowing agent in the cells as they are formed.
The purpose of the surfactant in the foamable composition is to help ensure the formation of a cellular structure that is conducive to good thermal insulation properties. The surfactant(s) tend to hold the blowing agent within the foam as the liquid foamable mixture solidifies and to thereby aid in the formation of smaller, more regular cells. If surfactant is not used in the foaming composition, the bubbles tend to simply pass through the liquid mixture without forming a foam or forming a foam with undesirably large, irregular cells.
In addition to the important performance characteristics mentioned above, it has become increasingly important for the blowing agent(s) used in foamable compositions to have low global warming potential. Previous applications illustrate the use of hydrohaloolefins (HFOs) as desirable blowing agents, particularly trans-1,3,3,3-tetrafluoropropene (HFO-1234ze(E)) and trans-1-chloro-3,3,3-trifluoropropene (HCFO-1233zd(E)). Processes for the manufacture of trans-1,3,3,3-tetrafluoropropene are disclosed in U.S. Pat. Nos. 7,230,146 and 7,189,884. Processes for the manufacture of trans-1-chloro-3,3,3-trifluoropropene are disclosed in U.S. Pat. Nos. 6,844,475 and 6,403,847.
It is convenient in many applications to provide the components for polyurethane or polyisocyanurate foams in pre-blended formulations. Most typically, the foam formulation is pre-blended into two components. The polyisocyanate and optionally isocyanate compatible raw materials, including but not limited to certain blowing agent(s) and non-reactive surfactant(s), comprise the first component, commonly referred to as the “A” component or “A side.” A polyol or mixture of polyols, one or more surfactant(s), one or more catalyst(s), one or more blowing agent(s), and other optional component(s), including but not limited to flame retardants, colorants, compatibilizers, and solubilizers, comprise the second component, commonly referred to as the “B” component or “B side.” Accordingly, polyurethane or polyisocyanurate foams are readily prepared by bringing together the A side and the B side components either by hand mix for small preparations and, preferably, machine mix techniques to form blocks, slabs, laminates, pour-in-place panels and other items, spray applied foams, froths, and the like. Optionally, other ingredients such as fire retardants, colorants, auxiliary blowing agents, and other polyols can be added to the mixing head or reaction site. Most conveniently, however, they are all incorporated into one B component.